Thermally bonded fabrics and method of making same

ABSTRACT

A method for producing a nonwoven fabric comprises passing a fiber web through a pair of rollers to obtain a thermally bonded fabric with a high percentage of bond areas. The high percentage of bond areas is formed by an engraved pattern on at least one of the rollers. The engraved pattern has a high percentage of bond point areas and wide bond point angles. The nonwoven fabric has increased tensile strength, elongation, abrasion resistance, flexural rigidity, and/or softness.

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to U.S. provisional applicationserial No. 60/254,747 filed on Dec. 11, 2000, which is incorporated byreference herein in its entirety.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

[0002] Not applicable.

REFERENCE TO MICROFICHE APPENDIX

[0003] Not applicable.

FIELD OF THE INVENTION

[0004] This invention relates to nonwoven fabrics formed from polyolefinpolymers and methods of making the fabrics.

BACKGROUND OF THE INVENTION

[0005] Fabrics made from fibers include both woven and nonwoven fabrics.Nonwoven fabrics are used for sanitary and medical uses includinghospital gowns, diaper linings, and sanitary wipes. Many processes forproducing bonded nonwoven fabrics exist. For example, one can apply heatand pressure for bonding at limited areas of a nonwoven web by passingit through the nip between heated calender rolls either or both of whichmay have patterns of lands and depressions on their surfaces. Duringsuch a bonding process, depending on the types of fibers making up thenonwoven web, the bonded regions may be formed autogenously, i.e., thefibers of the web are melt fused at least in the pattern areas, or withthe addition of an adhesive. The advantages of thermally bonded nonwovenfabrics include low energy costs and speed of production.

[0006] Nonwoven fabrics also can be made by a number of other methods,e.g., spunlacing or hydrodynamically entangling (as disclosed in U.S.Pat. No. 3,485,706 and U.S. Pat. No. 4,939,016); by carding andthermally bonding staple fibers; by spunbonding continuous fibers in onecontinuous operation; or by melt blowing fibers into fabric andsubsequently calendering or thermally bonding the resultant web.

[0007] Various properties of nonwoven fabrics determine the suitabilityof nonwoven fabrics for different applications. Nonwoven fabrics can beengineered to have different combinations of properties to suitdifferent needs. Variable properties of nonwoven fabrics include liquidhandling properties such as wettability, distribution, and absorbency,strength properties such as tensile strength and tear strength, softnessproperties, durability properties such as abrasion resistance, andaesthetic properties.

[0008] Polypropylene has been the primary polymer for nonwovens becauseof its cost, high strength, and processability. However, polypropylenenonwovens generally do not have a soft, cotton-like feel. As such,polyethylene nonwovens have gained interest. Polyethylenes producesofter fabrics but may have relatively low tensile strength and abrasionresistance.

[0009] Although nonwoven fabric properties such as liquid handlingproperties, strength properties, softness properties and durabilityproperties, are normally of primary importance in designing nonwovenfabrics, the appearance and feel of nonwoven fabrics are often criticalto the success of a nonwoven fabric product. The appearance and feel ofnonwoven fabrics is particularly important for nonwoven fabrics whichform exposed portions of products. For example, it is often desirablethat the outer covers of nonwoven fabric products have a cloth-like feeland a pleasing decorative design.

[0010] Despite the advances in the art described above, there is still aneed for improved nonwoven fabrics and methods of their manufacture. Inparticular, there is a need for nonwoven fabrics with improved: tensilestrength, elongation, abrasion resistance and softness as defined byfabric flexural rigidity.

SUMMARY OF THE INVENTION

[0011] Embodiments of the invention meet the above need by one or moreof the following aspects of the invention. In one aspect, the inventionrelates to a method for producing a nonwoven fabric with increasedtensile strength, elongation, abrasion resistance, flexural rigidity,and/or softness. The method comprises passing a fiber web through a pairof rollers to obtain a thermally bonded fabric with a high percentage ofbond areas. The high percentage of bond areas is formed by an engravedpattern on at least one of the rollers. The engraved pattern has a highpercentage of bond point areas and/or wide bond point angles.

[0012] In some embodiments, the percentage of bond areas of the fabricis at least about 16 percent, at least about 20 percent, or at leastabout 24 percent. The bond point angel is about 20° or higher, about 35°or higher, about 37° or higher, about 42° or higher, or about 46° orhigher. The engrave pattern has at least about 1.55×10⁵ bond points persquare meter, at least about 2.31×10⁵ bond points per square, at leastabout 3.1×10⁵ bond points per square meter, at least about 3.44×10⁵ bondpoints per square meter, at least about 4.6×10⁵ bond points per squaremeter, or at least about 4.65×10⁵ bond points per square meter. Thefiber web may comprise polyethylene, which may be a homopolymer ofethylene or a copolymer of ethylene and a comonomer. The polyethylenemay be obtained in the presence of a single site catalyst, such as ametallocene catalyst or a constrained geometry catalyst.

[0013] In another aspect, the invention relates to a non-woven fabricmade by the method described herein. The non-woven fabric comprises apolymer and is characterized by a high percentage of bond area and ahigh abrasion resistance. In some embodiments, the polymer ispolyethylene, which may be a homopolymer of ethylene or a copolymer ofethylene and a comonomer. The polyethylene may be obtained in thepresence of a single site catalyst, such as a metallocene catalyst or aconstrained geometry catalyst. In other embodiments, the percentage ofbond areas of the fabric is at least about 16 percent, at least about 20percent, or at least about 24 percent.

[0014] Various aspects of the invention and advantages provided by theembodiments of the invention are apparent with the followingdescription.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015]FIG. 1 is a simplified diagram of a process for producing fabricsfor use in embodiments of the invention.

[0016]FIG. 2A is a fragmentary elevation view of the embossing rollillustrating one arrangement of the bond points.

[0017]FIG. 2B is a simplified view of a nonwoven fabric produced fromthe process of FIG. 1 and the engraved roll of FIG. 2A.

[0018] FIGS. 3A-3I are schematics of bond patterns for use inembodiments of the invention on an arbitrary scale.

[0019] FIGS. 4A-4I are micrographs of nonwoven fabrics produced from thebond patterns in FIGS. 3A-3I for PE1 resin used in Example 1.

[0020]FIG. 5 is a graph of normalized peak loads vs. temperature forfabrics produced from the bond patterns in FIGS. 3A-3I for PE1 resin.

[0021]FIG. 6 is a graph of percent elongation vs. temperature forfabrics produced from the bond patterns in FIGS. 3A-3I for PE2 resinused in Example 1.

[0022]FIG. 7 is a graph of typical stress-strain curves for threefabrics produced in Example 1.

[0023]FIG. 8 is a graph of abrasion resistance vs. temperature forfabrics produced from the bond patterns in FIGS. 3A-3I for PE1 resin.

[0024]FIG. 9 is a graph of flexural rigidity vs. temperature for fabricsproduced from the bond patterns in FIGS. 3A-3I for PE1 resin.

[0025] FIGS. 10A-10I are scanning electron microscope micrographs, at80× magnification, of bond points of nonwoven fabrics produced from bondpatterns in FIGS. 3A-3I for PE1 resin.

[0026] FIGS. 11A-11C are scanning electron microscope micrographs oftensile test fracture sites of nonwoven fabrics produced from bondpatterns in FIGS. 3A-3I for various resins.

[0027] FIGS. 12A-12B are scanning electron microscope micrographs ofabraded bond sites of nonwoven fabrics produced from bond patterns inFIGS. 3A-3I for various resins.

DESCRIPTION OF EMBODIMENTS OF THE INVENTION

[0028] Embodiments of the invention provide a method for producing anon-woven fabric by thermal bonding. The fabric has a high percentage ofbond areas which are produced by passing a fiber web through a pair ofrolls, with at least one of the rolls having an engraved pattern with ahigh percentage of bond point areas along with wide bond point angles.The term “nonwoven” as used herein means a web or fabric having astructure of individual fibers or threads which are randomly interlaid,but not in an identifiable manner as is the case for a knitted fabric.The term “bonding” as used herein refers to the application of force orpressure (separate from or in addition to that required or used to drawfibers to less than or equal to 50 denier) to fuse molten or softenedfibers together. In some embodiments, the bond strength is greater thanor equal to about 1,500 grams results. The term “thermal bonding” isused herein refers to the reheating of fibers and the application offorce or pressure (separate from or in addition to that required or usedto draw fibers to less than or equal to 50 denier) to effect the melting(or softening) and fusing of fibers. In some embodiments, the bondstrength is greater than or equal to about 2,000 grams results.Operations that draw and fuse fibers together in a single orsimultaneous operation or prior to any take-up roll (for example, agodet), for example, spunbonding, are not considered to be a thermalbonding operation.

[0029] A thermal bonding process for producing a non-woven fabric isillustrated in FIG. 1. Such a process or variations thereof isdescribed, for example, in the following U.S. Pat. Nos.: 5,888,438;5,851,935; 5,733,646; 5,654,088; 55,629,080; 5,494,736; 4,770,925;4,635,073; 4,631,933; 4,564,553; 4,315,965, which are incorporated byreference herein in their entirety. All such disclosed processes may beutilized in embodiments of the invention with or without modifications.

[0030] Referring to FIG. 1, a web forming system 10, such as a cardingsystem, is employed to initially form a fibrous web 12. The fibers arealigned predominantly in the machine direction of web formation, asindicated by arrow 13. Alternatively, a spunbond system could be used toproduce more random orientation of the fibers. The web 12 may bedirected through a preheating station 14. The preheated web is thenpassed to the pressure nip of a bonding station provided by opposedrolls 20 and 22. The roll 20 is a metal engraved roll and is heated to atemperature near the melting point of the fibers. The backup roll (i.e.,smooth roll) 22 is heated in a controlled manner to a temperature nearthe melting point of the fibers, preferably below the stick point ofsuch fibers. In some embodiments, the engraved pattern comprisescircles, although other shapes, such as ovals, squares, andrectangulars, may be used.

[0031] The engraved roll as illustrated in FIG. 2A contains areas, bondpoints, that are in intimate, compressed contact with a flat roll. Theseareas induce melting and create bond areas. The size of these areasdetermines the number of fibers bonded at a single point and also thetotal area of the fabric that contains non-fibrous integrity. The numberof fibers connected at one bond point can influence its overallstrength, but also can contribute to its overall stiffness. There arethree factors of an engraved pattern that effect the overall propertiesof a nonwoven fabric. They include bond area, bond point or side-wallangle, and the concentration of bond points usually stated as points persquare unit area.

[0032] The engraved pattern on the roll is produced via bond points.These points extend from the engraved roll and when in contact with theflat roll, produce a bonded area. Generally the bond points produce apattern on the nonwoven fabric, such as seen in FIG. 2B. The bond pointsof an engraved pattern are generally expressed in terms of bond pointsper square area. In a preferred embodiment, the engraved pattern hasabout 1.55×10⁵ bond points per square meter (100 bond points per squareinch), preferably about 2.31×10⁵ bond points per square meter (149 bondpoints per square inch), more preferably about 3.10×10⁵ bond points persquare meter (200 bond points per square inch), or about 3.44×10⁵ bondpoints per square meter (222 bond points per square inch), or about4.60×10⁵ bond points per square meter (297 bond points per square inch),or about 4.65×10⁵ bond points per square meter (300 bond points persquare inch). Higher bond points per square meter such as 5.42×10⁵,6.20×10⁵, 7.75×10⁵, 9.30×10⁵, or more, (per square inch, such as 350,400, 500, 600, or more) also may be feasible.

[0033] The bond point is made up of a bond point angle and bond area.Referring to FIGS. 3A-I, various bond point patterns of different bondpoint angles and bond areas are shown. Bond point angle refers to theangle at which the bond point extends from the engraved roll. The bondpoint angle is about 20 degrees or higher, preferably about 35 degreesor higher, more preferably about 37 degrees or higher, most preferablyabout 42 degrees or higher, and still most preferably about 46 degreesor higher. FIG. 3A is for bond pattern 1 having a 46° angle, 20 percentbond area, 3.44×10⁵ pts/m² (222 pts/in²), base width of 1.7×10⁻³ m(0.067 inch), base height of 4.32×10⁻⁴ m (0.017 inch), and a point widthof 7.62×10⁻⁴ m (0.03 inch). FIG. 3B is for bond pattern 2 having a 20°angle, 16 percent bond area, 3.44×10⁵ pts/m² (222 pts/in²), base widthof 1.7×10⁻³ m (0.067 inch), base height of 4.32×10⁻⁴ m (0.017 inch), anda point width of 6.86×10⁻⁴ m (0.027 inch). FIG. 3C is for bond pattern 3having a 20° angle, 24 percent bond area, 3.44×10⁵ pts/m² (222 pts/in²),base width of 1.7×10⁻³ m (0.067 inch), base height of 4.32×10⁻⁴ m (0.017inch), and a point width of 8.38×10⁻⁴ m (0.033 inch). FIG. 3D is forbond pattern 4 having a 20° angle, 20 percent bond area, 2.31×10⁵ pts/m²(149 pts/in²), base width of 1.7×10⁻³ m (0.067 inch), base height of4.32×10⁻⁴ m (0.017 inch), and a point width of 9.30×10⁻⁴ m (0.0366inch). FIG. 3E is for bond pattern 5 having a 20° angle, 20 percent bondarea, 4.60×10⁵ pts/m² (297 pts/in²), base width of 1.7×10⁻³ m (0.067inch), base height of 4.32×10⁻⁴ m (0.017 inch), and a point width of6.60×10⁻⁴ m (0.026 inch). FIG. 3F is for bond pattern 6 having a 42°angle, 16 percent bond area, 3.44×10⁵ pts/m² (222 pts/in²), base widthof 1.7×10⁻³ m (0.067 inch), base height of 4.32×10⁻⁴ m (0.017 inch), anda point width of 6.86×10⁻⁴ m (0.027 inch). FIG. 3G is for bond pattern 7having a 37° angle, 24 percent bond area, 3.44×10⁵ pts/m² (222 pts/in²),base width of 1.7×10⁻³ m (0.067 inch), base height of 4.32×10⁻⁴ m (0.017inch), and a point width of 8.38×10⁻⁴ m (0.033 inch). FIG. 3H is forbond pattern 8 having a 46° angle, 20 percent bond area, 2.31×10⁵ pts/m²(149 pts/in²), base width of 1.7×10⁻³ m (0.067 inch), base height of4.32×10⁻⁴ m (0.017 inch), and a point width of 9.3×10⁻⁴ m (0.0366 inch).FIG. 3I is for bond pattern 9 having a 35° angle, 20 percent bond area,4.60×10⁵ pts/m² (297 pts/in²), base width of 1.7×10⁻³ m (0.067 inch),base height of 4.32×10⁻⁴ m (0.017 inch), and a point width of 6.60×10⁻⁴m (0.026 inch).

[0034] Bonded areas and unbonded areas make up the nonwoven fabric.Bonded areas may be defined as the percentage of the surface area of thenonwoven fabric that is covered by a bond produced by the bond point Thebond area in embodiments of the invention is preferably at least 16percent, more preferably at least 20 percent and most preferably atleast 24 percent, 30 percent, 35 percent, 40 percent, 45 percent, 50percent or more.

[0035] Fiber and Nonwoven Fabric Fabrication

[0036] A web forming system generally includes processes for producingfibers which can be thermally bonded to form fabrics include dry laid,wet laid, and polymer laid or any other processes. In some embodiments,the fibers are produced by spunbond, meltblown or carded stapleprocesses. These processes are further described in the following UnitedStates Patents, which are hereby incorporated by reference in theirentirety: U.S. Pat. Nos. 3,338,992; 3,341,394; 3,276,944; 3,502,538;3,978,185; and 4,644,045. In general, the spunbond process uses a highpowered vacuum chamber to increase the velocity of the fibers in orderto decrease the fiber's diameters to produce a continuous fiber. Themeltblown process blows air down from above and uses surface forces todrag the fibers to higher velocities to produce very low deniernon-continuous fibers.

[0037] Conventional spunbond processes are described in U.S. Pat. Nos.3,825,379; 4,813,864; 4,405,297; 4,208,366; and 4,334,340 all of whichare incorporated by reference herein in their entirety. The spunbondingprocess is one which is well known in the art of fabric production.Generally, continuous fibers are extruded, laid on an endless belt, andthen bonded to each other, and often times to a second layer such as amelt blown layer, often by a heated calendar roll, or addition of abinder. An overview of spunbonding may be obtained from L. C. Wadsworthand B. C. Goswami, Nonwoven Fabrics: “Spunbonded and Melt BlownProcesses” proceedings Eight Annual Nonwovens Workshop, Jul. 30-Aug. 3,1990, sponsored by The Textiles and Nonwovens Development Center(hereinafter “TANDEC”), University of Tennessee, Knoxville, Tenn.

[0038] The term “meltblown” is used herein to refer to fibers formed byextruding a molten thermoplastic polymer composition through a pluralityof fine, usually circular, die capillaries as molten threads orfilaments into converging high velocity gas streams (e.g. air) whichfunction to attenuate the threads or filaments to reduced diameters.Thereafter, the filaments or threads are carried by the high velocitygas streams and deposited on a collecting surface to form a web ofrandomly dispersed meltblown fibers with average diameters generallysmaller than 10 microns.

[0039] The term “spunbond” is used herein to refer to fibers formed byextruding a molten thermoplastic polymer composition as filamentsthrough a plurality of fine, usually circular, die capillaries of aspinneret with the diameter of the extruded filaments then being rapidlyreduced and thereafter depositing the filaments onto a collectingsurface to form a web of randomly dispersed spunbond fibers with averagediameters generally between about 7 and about 30 microns.

[0040] Nonwovens can be produced by numerous methods. Most methodsinclude substantially the same basic procedures: (1) material selection;(2) web formation; (3) web consolidation; and (4) web finishing.Material selection provides the properties suitable for the application.The web is formed from fibers of the selected materials. The web is thenbonded to form a fabric and the fabric is finished to produce the finalproduct for cutting and folding.

[0041] The diameter of the fiber affects properties of the fabricincluding strength and flexural rigidity. Fiber diameter can be measuredand reported in a variety of fashions. Generally, fiber diameter ismeasured in denier per filament. Denier is a textile term which isdefined as the grams of the fiber per 9000 meters of that fiber'slength. Monofilament generally refers to an extruded strand having adenier per filament greater than 15, usually greater than 30. Finedenier fiber generally refers to fiber having a denier of about 15 orless. Microdenier (i.e., microfiber) generally refers to fiber having adiameter not greater than about 100 micrometers. For the fibersdisclosed herein, the diameter can be widely varied, with little impactupon the fiber's elasticity. However, the fiber denier can be adjustedto suit the capabilities of the finished article and as such, wouldpreferably be: from about 0.5 to about 30 denier/filament for meltblown; from about 1 to about 30 denier/filament for spunbond; and fromabout 1 to about 20,000 denier/filament for continuous wound filament.One can convert the fiber diameter in denier to meter according to theequation:${{fiber}\quad {diameter}\quad ({meter})} = {11.89 \times 10^{- 6} \times {\sqrt{\frac{{fiberdiamter}\quad ({denier})}{{fiberdensity}\quad \left( {g\text{/}{cc}} \right)}}.}}$

[0042] Other fiber properties that influence the fabric's finalproperties include the fiber's orientation, crystallinity, diameter andcooling rates. The strength of the bond is a limiting factor in nonwovenfabric strength. Lower fiber orientation allows for greater amounts ofmelting during bonding, causing stronger bonding regions. In addition,high amounts of orientation induced by drawing a polymer causes highamounts of shrinkage during thermal bonding making processabilitydifficult.

[0043] Crystalline portions of a fiber are particularly of interest tothe thermal bonding process due to the melting that occurs. The degreeof melting and flow significantly impacts the bond strength. Less stablecrystals melt first; followed by the more stable or oriented crystals ifenough heat is transferred to the polymer. Because of the short durationof heat transfer to the bond area, only a fraction of the crystals melt.

[0044] After the web has been loosely formed, the individual fibers needto be bonded together. Web consolidation provides strength and rigidityto the fabric. Ways to consolidate the web include mechanical, chemical,and thermal bonding. Mechanical consolidation is accomplished byentangling fibers at various points in the web, including needlepunching, stitch bonding, spunlacing, or any other mechanicalconsolidation process. Chemical bonding involves spraying or saturatingthe web with an adhesive such as latex. Thermal bonding of the web is acommon bonding technique and include point-calender, ultrasonic andradian-heat bonding. In some embodiments, point-calender bonding is usedand comprises passing the web through two heated rolls that are inintimate contact. One roll is male-patterned engraved and the other is aflat roll. The fibers melt and flow over one another. Upon cooling, thefabric is formed.

[0045] As a web of fibers is pulled into calender there are manythermomechanical processes of different magnitudes that occur. Theseprocesses include: conductive heat transfer; heat of deformation; flowof melted polymer; diffusion; and the Clapeyron effect.

[0046] Conductive heat transfer is transported across the steel roll,fabric interface. The amount of heat transferred by conduction isproportional to the temperature of the steel rolls and the amount oftime the web spends under the bond pin (roll speed). Also adding heat tothe system is the heat of deformation. Due to high pressures between thesteel rolls, the web is formed into a different shape very quickly andmechanical work is done on the system. This mechanical work istransferred to heat. These two forms of heat raise the temperature ofthe web between the rolls and is highest under the bond pin. An equationassuming that all of the mechanical work transfers to heat is given by:

[F(s)ds]=VρC _(p) ΔT+fΔH _(f) χΔV

[0047] where F(s)ds is the force exerted on the web over a distance ds,a is the fraction of mechanical work converted to heat, V is the volumeof the web, χ is the crystallinity, and f is the fraction of crystalsthat melt. The first term on the right side is the amount of heat usedto increase the temperature and the second term describes the amount ofheat that melts the polymer crystals.

[0048] When the temperature reaches its melting point, the high pressureunder the pins causes the melt to flow outside to an area of lowerpressure. Also while in the molten state, the polymer self-diffuses.Upon exiting the calender, the melt solidifies and mechanically locksthe fibers at the bond point. These two phenomena fuse together severalfibers at a bond point and turn the web into a fabric. The diffusionpenetration distance for polymers during the bonding process is almostnegligible. The penetration distance is given by:

R=[t(2×D)]^(½)

[0049] where R is the penetration distance, t is the time, and D is theself-diffusion coefficient. In general, most polymers have a diffusioncoefficient of a magnitude of 10⁻¹⁵ and spend 10 to 40 millisecondsunder the bond pins. Using these rough numbers it is calculated that thepenetration distance is only between 45 Å and 100 Å. Considering mostfibers used in thermal bonding are about 20 microns in diameter, thefibers only diffuse 0.00000225 percent of their total diameter.Therefore, the mechanical interlocking of the polymer melt around thefibers in the bonding area is likely to be the dominating force holdingthe fibers together at the bond point.

[0050] The increased pressure under the bond pins leads to an increasein melting temperature otherwise known as the Clapeyron Effect. Theeffect of pressure increases the melting point of polypropylene 38K/kbar or 0.38° C./Mpa. Using a typical pressure under the bond pin,polypropylene's melting point increases about 10° C. Polyethylene'smelting temperature increases only about 5° C. under typical bondingpressures.

[0051] Several factors of the point-bond hot calendering process affectfinal fabric properties including temperature, pressure, speed, rolldiameter and engraved pattern. The choice of temperature is mainly afunction of the material, but it should be noted that the total energytransfer to the web is a function of temperature, pressure, rolldiameter, and line speed. If the temperature is chosen too low, then theweb is under-bonded and the fabric strength tends to be weak. If theroll temperature is too high then the web is over-bonded and theresulting fabric is too stiff or the web completely melts and sticks tothe roll.

[0052] The effect of pressure applied to the fabric is small, but notnegligible. At low pressures, the bonding of the web is poor andstrength is, therefore, poor. As pressure increases, the fabric strengthis a function of both bonding temperature and pressure. At very highpressure, though, the fabric strength reaches a maximum and then beginsto decrease with increasing pressure. Below this pressure the strengthincreases continuously up to the melting point of the polymer.

[0053] The speed and diameter of the bond roll affect the total time ofheat transfer to the web. Larger bond roll diameters allow for moreintimate contact with the heated rolls than do smaller rolls. Hencethere is more heat transferred to the web. In the same manner, slowspinning rolls have more contact time then fast spinning rolls.

[0054] The amount of time a fabric spends in the nip (intimate contactregion) may be expressed as:

t=AC _(O) ^(½) R ^(½) V ⁻¹

[0055] t=time

[0056] R=radius of bond roll

[0057] V=velocity of bond roll$A = {\sqrt{\frac{C_{O} - C_{N}}{C_{O}}} + \sqrt{\frac{C_{R} - C_{N}}{C_{O}}}}$

[0058] where C_(O) is the original web thickness, C_(N) is the thicknessbetween the bond rolls, and C_(R) is the thickness after compression inthe bond roll.

[0059] The shape of the fiber is not limited and can be any suitableshape. For example, typical fiber have a circular cross sectional shape,but sometimes fibers have different shapes, such as a trilobal shape, ora flat (i.e., “ribbon” like) shape.

[0060] After a thermally bonded fabric has eluded from the bond pins,cooling and solidifying of the bond regions occurs. The quench rate ofthe fabric and more specifically the bonding region may have an impacton the final fabric properties.

[0061] Important fabric properties include strength, elongation, peakload, abrasion and flexural rigidity. The strength or tenacity andelongation of a nonwoven fabric is important to both post productionprocesses and the consumer. The more strength and elasticity a fabrichas, the faster it can be combined with other materials into a finalconsumer product. Another property of a nonwoven fabric is its abilityto resist abrasion. When an abrasive surface is applied to a nonwovenfabric, fibers are pulled from the surface and cause fuzz or pilling toform on the surface. As such, high abrasion resistance is desirable fornonwoven fabrics. Still another important property of a material that isworn by humans and placed against the skin is its stiffness. Thisproperty can be measured by flexural rigidity or handfeel evaluations.

[0062] Fiber-Forming Polymers

[0063] Any fiber-forming polymers, especially those which can bethermally bonded, may be used in embodiments of the invention. Forexample, suitable polymers include, but are not limited to, α-olefinhomopolymers and interpolymers comprising polypropylene,propylene/C₄-C₂₀ α-olefin copolymers, polyethylene, and ethylene/C₃-C₂₀α-olefin copolymers, the interpolymers can be either heterogeneousethylene/α-olefin interpolymers or homogeneous ethylene/α-olefininterpolymers, including the substantially linear ethylene/α-olefininterpolymers. Also included are aliphatic α-olefins having from 2 to 20carbon atoms and containing polar groups. Suitable aliphatic α-olefinmonomers which introduce polar groups into the polymer include, forexample, ethylenically unsaturated nitriles such as acrylonitrile,methacrylonitrile, ethacrylonitrile, etc.; ethylenically unsaturatedanhydrides such as maleic anhydride; ethylenically unsaturated amidessuch as acrylamide, methacrylamide etc.; ethylenically unsaturatedcarboxylic acids (both mono- and difunctional) such as acrylic acid andmethacrylic acid, etc.; esters (especially lower, e.g. C₁-C₆, alkylesters) of ethylenically unsaturated carboxylic acids such as methylmethacrylate, ethyl acrylate, hydroxyethylacrylate, n-butyl acrylate ormethacrylate, 2-ethyl-hexylacrylate, or ethylene-vinyl acetatecopolymers etc.; ethylenically unsaturated dicarboxylic acid imides suchas N-alkyl or N-aryl maleimides such as N-phenyl maleimide, etc.Preferably such monomers containing polar groups are acrylic acid, vinylacetate, maleic anhydride and acrylonitrile. Halogen groups which can beincluded in the polymers from aliphatic α-olefin monomers includefluorine, chlorine and bromine; preferably such polymers are chlorinatedpolyethylenes (CPEs). Polymers, such as polyester and nylon, also may beused.

[0064] Heterogeneous interpolymers are differentiated from thehomogeneous interpolymers in that in the latter, substantially all ofthe interpolymer molecules have the same ethylene/comonomer ratio withinthat interpolymer, whereas heterogeneous interpolymers are those inwhich the interpolymer molecules do not have the same ethylene/comonomerratio. The term “broad composition distribution” used herein describesthe comonomer distribution for heterogeneous interpolymers and meansthat the heterogeneous interpolymers have a “linear” fraction and thatthe heterogeneous interpolymers have multiple melting peaks (i.e.,exhibit at least two distinct melting peaks) by DSC. The heterogeneousinterpolymers have a degree of branching less than or equal to 2methyls/1000 carbons in about 10 percent (by weight) or more, preferablymore than about 15 percent (by weight), and especially more than about20 percent (by weight). The heterogeneous interpolymers also have adegree of branching equal to or greater than 25 methyls/1000 carbons inabout 25 percent or less (by weight), preferably less than about 15percent (by weight), and especially less than about 10 percent (byweight).

[0065] The heterogeneous polymer component can be an α-olefinhomopolymer preferably polyethylene or polypropylene, or, preferably, aninterpolymer of ethylene with at least one C₃-C₂₀ α-olefin and/or C₄-C₁₈dienes. Heterogeneous copolymers of ethylene, and propylene, 1-butene,1-hexene, 4-methyl-1-pentene and 1-octene are especially preferred.

[0066] Linear low density polyethylene (LLDPE) is produced in either asolution or a fluid bed process. The polymerization is catalytic.Ziegler Natta and single-site metallocene catalyst systems have beenused to produce LLDPE. The resulting polymers are characterized by anessentially linear backbone. Density is controlled by the level ofcomonomer incorporation into the otherwise linear polymer backbone.Various alpha-olefins are typically copolymerized with ethylene inproducing LLDPE. The alpha-olefins which preferably have four to eightcarbon atoms, are present in the polymer in an amount up to about 10percent by weight. The most typical comonomers are butene, hexene,4-methyl-1-pentene, and octene. The comonomer influences the density ofthe polymer. Density ranges for LLDPE are relatively broad, typicallyfrom 0.87-0.95 g/cc (ASTM D-792).

[0067] Linear low density polyethylene melt index is also controlled bythe introduction of a chain terminator, such as hydrogen or a hydrogendonator. The melt index, measured according to ASTM D-1238 Condition190° C./2.16 kg (formerly known as “Condition E” and also known as“I₂”), for a linear low density polyethylene can range broadly fromabout 0.1 to about 150 g/10 min. For purposes of the present invention,the LLDPE should have a melt index of greater than 10, and preferably 15or greater for spunbonded filaments. Particularly preferred are LLDPEpolymers having a density of 0.90 to 0.945 g/cc and a melt index ofgreater than 25.

[0068] Examples of suitable commercially available linear low densitypolyethylene polymers include the linear low density polyethylenepolymers available from Dow Chemical Company, such as the ASPUNTM seriesof fibergrade resins, Dow LLDPE 2500 (55 MI, 0.923 density), Dow LLDPEType 6808A (36MI, 0.940 density), and the EXACTTM series of linear lowdensity polyethylene polymers from Exxon Chemical Company, such asEXACT™ 2003 (31 MI, density 0.921).

[0069] The homogeneous polymer component can be an α-olefin homopolymerpreferably polyethylene or polypropylene, or, preferably, aninterpolymer of ethylene with at least one C₃-C₂₀ α-olefin and/or C₄-Cl₈dienes. Homogeneous copolymers of ethylene, and propylene, 1-butene,1-hexene, 4-methyl-1-pentene and 1-octene are especially preferred.

[0070] The relatively recent introduction of metallocene-based catalystsfor ethylene/α-olefin polymerization has resulted in the production ofnew ethylene interpolymers known as homogeneous interpolymers.

[0071] The homogeneous interpolymers useful for forming fibers describedherein have homogeneous branching distributions. That is, the polymersare those in which the comonomer is randomly distributed within a giveninterpolymer molecule and wherein substantially all of the interpolymermolecules have the same ethylene/comonomer ratio within thatinterpolymer. The homogeneity of the polymers is typically described bythe SCBDI (Short Chain Branch Distribution Index) or CDBI (CompositionDistribution Branch Index) and is defined as the weight percent of thepolymer molecules having a comonomer content within 50 percent of themedian total molar comonomer content. The CDBI of a polymer is readilycalculated from data obtained from techniques known in the art, such as,for example, temperature rising elution fractionation (abbreviatedherein as “TREF”) as described, for example, in Wild et al, Journal ofPolymer Science, Poly. Phys. Ed., Vol. 20, p. 441 (1982), in U.S. Pat.No. 4,798,081, or as is described in U.S. Pat. No. 5,008,204, thedisclosure of which is incorporated herein by reference. The techniquefor calculating CDBI is described in U.S. Pat. No. 5,322,728 and in U.S.Pat. No. 5,246,783 or in U.S. Pat. No. 5,089,321 the disclosures of allof which are incorporated herein by reference. The SCBDI or CDBI for thehomogeneous interpolymers used in the present invention is preferablygreater than about 30 percent, especially greater than about 50 percent,70 percent or 90 percent.

[0072] The homogeneous interpolymers used in this invention essentiallylack a measurable “high density” fraction as measured by the TREFtechnique (i.e., the homogeneous ethylene/α-olefin interpolymers do notcontain a polymer fraction with a degree of branching less than or equalto 2 methyls/1000 carbons). The homogeneous interpolymers also do notcontain any highly short chain branched fraction (i.e., they do notcontain a polymer fraction with a degree of branching equal to or morethan 30 methyls/1000 carbons).

[0073] The substantially linear ethylene/α-olefin polymers andinterpolymers are also homogeneous interpolymers but are further hereindefined as in U.S. Pat. No. 5,272,236, and in U.S. Pat. No. 5,272,872,the entire contents of which are incorporated by reference. Suchpolymers are unique however due to their excellent processability andunique rheological properties and high melt elasticity and resistance tomelt fracture. These polymers can be successfully prepared in acontinuous polymerization process using the constrained geometrymetallocene catalyst systems.

[0074] The term “substantially linear” ethylene/α-olefin interpolymermeans that the polymer backbone is substituted with about 0.01 longchain branches/1000 carbons to about 3 long chain branches/1000 carbons,more preferably from about 0.01 long chain branches/1000 carbons toabout 1 long chain branches/1000 carbons, and especially from about 0.05long chain branches/1000 carbons to about 1 long chain branches/1000carbons.

[0075] Long chain branching is defined herein as a chain length of atleast one carbon more than two carbons less than the total number ofcarbons in the comonomer, for example, the long chain branch of anethylene/octene substantially linear ethylene interpolymer is at leastseven (7) carbons in length (i.e., 8 carbons less 2 equals 6 carbonsplus one equals seven carbons long chain branch length). The long chainbranch can be as long as about the same length as the length of thepolymer back-bone. Long chain branching is determined by using ¹³Cnuclear magnetic resonance (NMR) spectroscopy and is quantified usingthe method of Randall (Rev. Macromol. Chem. Phys., C29 (2&3), p.285-297), the disclosure of which is incorporated herein by reference.Long chain branching, of course, is to be distinguished from short chainbranches which result solely from incorporation of the comonomer, so forexample the short chain branch of an ethylene/octene substantiallylinear polymer is six carbons in length, while the long chain branch forthat same polymer is at least seven carbons in length.

[0076] Additional suitable polymers are disclosed in the following U.S.Pat. No.: 6,316,549; 6,281,289; 6,248,851; 6,194,532; 6,190,768;6,140,442; 6,037,048; 5,603,888; 5,185,199, and 5,133,917, all of whichare incorporated by reference herein in their entirety.

[0077] Examples of commercial fiber-forming polyethylene include ASPUN™6806A (melt index: 105.0 g/10min.; density: 0.930 g/cc), ASPUN™ 6842A(melt index: 30.0 g/10 min.; density: 0.955 g/cc), ASPUN™ 681A (meltindex: 27.0 g/10min.; density: 0.941 g/cc), ASPUN™ 6830A (melt index:18.0 g/10min.; density: 0.930 g/cc), ASPUN™ 6831A (melt index: 150.0g/10min.; density: 0.930 g/cc), and ASPUN™ 8635A (melt index: 17.0g/10min.; density: 0.950 g/cc), all available from The Dow ChemicalCompany, Midland, Mich. These linear low density polyethylene may beblended with a homogeneous substantially linear ethylene polymer, suchas AFFINITY™ resin from The Dow Chemical Company.

[0078] Examples of commercial fiber-forming polypropylene includehomopolypropylene designated as 5A10 (melt flow rate: 1.4 g/10min.;flexural modulus: 1585 MPa (230,000 psi)); 5A28 (melt flow rate: 3.0g/10min.; flexural modulus:: 1585 MPa (230,000 psi)); 5A66V (melt flowrate: 4.6 g/10min.; flexural modulus: 1654 MPa (240,000 psi)); 5E17V(melt flow rate: 20.0 g/10min.; flexural modulus: 1344 MPa (195,000psi)); 5E40 (melt flow rate: 9.6 g/10min.; flexural modulus: 1378 MPa(200,000 psi)); NRD5-1258 (melt flow rate: 100.0 g/10min.; flexuralmodulus: 1318 MPa (191,300 psi)); NRD5-1465 (melt flow rate: 20.0g/10min.; flexural modulus: 1344 MPa (195,000 psi)); NRD5-1502 (meltflow rate: 1.6 g/10min.; flexural modulus: 1347 MPa (195,500 psi));NRD5-1569 (melt flow rate: 4.2 g/10min.; flexural modulus: 1378 MPa(200,000 psi)); NRD5-1602 (melt flow rate: 40.0 g/10min.; flexuralmodulus: 1172 MPa (170,000 psi)); SRD5-1572 (melt flow rate: 38.0g/10min.; flexural modulus: 1298 MPa (188,400 psi)); SRD5-1258 (meltflow rate: 25.0 g/10min.), and INSPIRE™ resin (melt flow rates rangingfrom 1.8 to about 25 g/10min.), all available from The Dow ChemicalCompany. The melt flow rate is measured according to ASTM D 1238 (230°C./2.16 kg), and flexural modulus according to ASTM D 790A. It should beunderstood that resins from other companies, such as Exxon, Bassel,Mitsui, etc., also may be used.

[0079] Additives such as antioxidants (e.g., hindered phenolics such asIRGANOX™ 1010 or IRGANOX™ 1076 supplied by Ciba Geigy), phosphites(e.g., IRGAFOS™ 168 also supplied by Ciba Geigy), cling additives (e.g.,PIB), pigments, colorants, fillers, and the like, can also be includedin the fiber materials disclosed herein.

[0080] Similarly, the polymers disclosed herein can be admixed withother polymers to modify characteristics such as elasticity,processability, strength, thermal bonding, or adhesion, to the extentthat such modification does not adversely affect the desired properties.

[0081] Some useful materials for modifying the polymers include, othersubstantially linear ethylene polymers as well as other polyolefins,such as high pressure low density ethylene homopolymer (LDPE),ethylene-vinyl acetate copolymer (EVA), ethylene-carboxylic acidcopolymers, ethylene acrylate copolymers, polybutylene (PB),ethylene/.alpha.-olefin polymers which includes high densitypolyethylene (HDPE), medium density polyethylene, polypropylene,ethylene-propylene interpolymers, ultra low density polyethylene(ULDPE), as well as graft-modified polymers involving, for example,anhydrides and/or dienes, or mixtures thereof.

[0082] Still other polymers suitable for modifying the polymers includesynthetic and natural elastomers and rubbers which are known to exhibitvarying degrees of elasticity. AB and ABA block or graft copolymers(where A is a thermoplastic endblock such as, for example, a styrenicmoiety and B is an elastomeric midblock derived, for example, fromconjugated dienes or lower alkenes), chlorinated elastomers and rubbers,ethylene propylene diene monomer (EDPM) rubbers, ethylene-propylenerubbers, and the like and mixtures thereof are examples of known priorart elastic materials contemplated as suitable for modifying the elasticmaterials disclosed herein.

[0083] Polypropylene can be blended with a lower melting polymer such aspolyethylene to increase the strength in the bond region. In the sameway LLDPE can be blended with a low melting/low density polyethylene toproduce the same results.

[0084] The initial chemical structure of the polymer used to producenonwovens has an affect on the fabric properties. A polymer's chemicalstructure impacts the polymer's density/crystallinity, viscosity, andmolecular weight distribution. Also, addition of two or more polymers tomake a blend can have a significant impact on the nonwoven properties.Fabric strength increases with increasing molecular weight distribution.The increase in MWD decreases the orientation of the fibers in thespinning process, causing greater melting during calendering.

[0085] The nonwoven fabrics in accordance with embodiments of theinvention have utility in a variety of applications. Suitableapplications include, but are not limited to, disposable personalhygiene products (e.g. training pants, diapers, absorbent underpants,incontinence products, feminine hygiene items and the like), disposablegarments (e.g. industrial apparel, coveralls, head coverings,underpants, pants, shirts, gloves, socks and the like) and infectioncontrol/clean room products (e.g. surgical gowns and drapes, face masks,head coverings, surgical caps and hood, shoe coverings, boot slippers,wound dressings, bandages, sterilization wraps, wipers, lab coats,coverall, pants, aprons, jackets, bedding items and sheets). Thenonwoven fabrics also may be used in manners taught in the followingU.S. Pat. Nos.: 6,316,687; 6,314,959; 6,309,736; 6,286,145; 6,281,289;6,280,573; 6,248,851; 6,238,767; 6,197,322; 6,194,532; 6,194,517;6,176,952; 6,146,568; 6,140,442; 6,093,665; 6,028,016; 5,919,177;5,912,194; 5,900,306; 5,830,810; and 5,798,167, all of which areincorporated by reference herein in their entirety.

EXAMPLES

[0086] The following examples exemplify some embodiments of theinvention. They do not limit the invention as otherwise described andclaimed herein. All numbers in the examples are approximate values. Inthe following examples, various nonwoven fabrics were characterized by anumber of methods. Performance data of these fabrics were also obtained.Most of the methods or tests were performed in accordance with an ASTMstandard, if applicable, or known procedures.

[0087] Preparation of Polymer Blends

[0088] A HAAKE twin screw extruder was used to produce polymer blends.The extruder has the following characteristics:

[0089] 6 heating zones with temperatures of 110° C., 120° C., 130° C.,135° C., 135° C., 135° C. respectively.

[0090] Two 18 mm diameter screws.

[0091] L/D=30

[0092] Melt temperature=146° C.

[0093] Die Pressure=2.64×10⁶ Pa (383 psi)

[0094] Torque=3.44×10⁷ Pa (5000 psi)

[0095] Speed=200 rpm

[0096] Preparation of Polymer Fibers

[0097] Fibers were produced by extruding the polymer using a one inchdiameter extruder which feeds a gear pump. The gear pump pushes thematerial through a spin pack containing a 40 micrometer (average poresize) sintered flat metal filter and a 108 hole spinneret. The spinneretholes have a diameter of 400 micrometers and a land length (i.e.,length/diameter or L/D) of 4/1. The gear pump is operated such thatabout 0.3 grams of polymer are extruded through each hole of thespinneret per minute. Melt temperature of the polymer varies dependingupon the molecular weight of the polymer being spun. Generally thehigher the molecular weight, the higher the melt temperature. Quench air(slightly above room temperature (about 24° C.) is used to help the meltspun fibers cool. The quench air is located just below the spinneret andblows air across the fiber line as it is extruded. The quench air flowrate is low enough so that it can barely be felt by hand in the fiberarea below the spinneret. The fibers are collected on godet rolls havinga diameter of about 0.152 m (6 inches). The godet roll's speed isadjustable, but for the experiments demonstrated herein, the godet'sspeed is about 1500 revolutions/minute. The godet rolls are locatedabout 3 meters below the spinneret die. Immediately following thespinning process, all fibers are cut into fibers of 0.0381 m (1.5inches) in length.

[0098] Preparation of Nonwoven Fabrics

[0099] Nonwoven fabric samples were produced on a laboratory calenderequipped with a hardened, chromed engraved steel roll according to theprocedures described herein. An engraved pattern contains a 20 percenttotal bonding area and 3.44×10⁵ bonding points per square meter (222bonding points per square inch). FIGS. 3A-3I schematically show variousbonding patterns along with their dimensions that were used inembodiments of the invention.

[0100] For each pattern design the following procedure was followed. Allfibers were 3 denier. The fibers were then fed into a carding machine.The fibers were pulled into the RotorRing by a vacuum and passed througha series of needles. The fibers were then neatly arranged for futurecarding by a high speed centrifuge. This process was repeated for eachsample. Next, the fibers were distributed evenly on a steel tray ofdimensions 10 cm by 40 cm a paper feed card encases the front end of thefiber web. This produces a web with a basis weight of 33 g/m² or 1oz/yd². The fiber web was placed between the moving, heated calenderrolls where the web was thermally bonded into a nonwoven fabric. Thestarting bond roll conditions were as follows:

[0101] Top (engraved) roll temperature—from about 110° C. (230° F.) toabout 121.1° C. (250° F.), which is the temperature described in thefigures and tables.

[0102] Bottom (smooth) roll temperature—from about 110° C. (230° F.) toabout 121.1° C. (250° F.), which is about 4° C. higher than the top rollto avoid sticking to the top roll.

[0103] Hydraulic pressure—from about 4.82×10⁶ Pa (700 psi) to about1.03×10⁷ Pa (1500 psi).

[0104] Roll Speed/dial setting=from about 3 to about 5 m/min.

[0105] Test Methods

[0106] The fabrics produced contain mostly machine direction alignment.There is very little cross direction alignment of the fibers.Characterization of fabrics and fiber orientation were conducted usingthe following technique:

[0107] 1. Optical micrographs were obtained from randomly selectedfabrics from this experiment. Both the top of the fabric and the bottomof the fabric were photographed at 40× magnification. Opticalmicrographs were also obtained from commercial Spunbond PP fabric madeat TANDEC in the same manner.

[0108] 2. The micrographs were transferred to Scion Imaging software anddivided into four quarters.

[0109] 3. The angles of the fibers in each quarter of the micrographswere measured with the machine direction being vertical (0°) and thecross direction being horizontal (90°).

[0110] Once all fibers were measured, the following equation was used toquantify the orientation:

F _(p)=2*avg.(cosθ)²−1

[0111] θ is the angle of the fiber and F_(p) is the orientationparameter is which a value of 0 corresponds to random orientation and avalue of 1 corresponds to perfect alignment in one direction.

[0112] The tensile strength of each fabric sample was investigated usingan Instron 4501 tensile tester. Line grip jaws were used to fasten thefabric to the Instron. The “Standard Test Method for Breaking Force andElongation of Textile Fabrics” (ASTM D 5035-90) was used with oneexception. The strips were not cut into 0.152 m (6 inch) strips but into0.101 m (4 inch) strips.

[0113] A standard abrasion procedure was developed comprising thefollowing steps using a Taber Abraser model 503 (RotaryPlatform-Double-Head Method) with an 8 compartment sample holder:

[0114] 1. The fabric was cut into 0.0762×0.0762 m (3×3 inch) pieces andlabeled.

[0115] 2. An adhesive backing was applied to the edges of the abradedsurface to prevent tearing at the edges.

[0116] 3. Samples were weighed individually to 4 decimal places.

[0117] 4. The samples were placed in the sample holder making sure notto cause any wrinkles or loose areas. The samples were arranged with themachine direction pointing at the center of the sample holder and theengraved pattern side facing up.

[0118] 5. The fabric samples were abraded for a determined amount ofcycles (100) using CO₂ rubber abrasion wheels. Masking tape made byAmerican Tape was applied to the abraded surface and then removed in asteady, but quick motion.

[0119] 6. The fabric was again weighed and recorded.

[0120] Any samples that tore or completely degraded during abrasion werethrown out and deleted from further testing.

[0121] Flexural rigidity was measured according to the designspecifications of ASTM method D 1388-64. A leveling bubble was placed onthe horizontal platform before measurements were taken to ensureconsistency. The length of overhang and the basis weight of the fabricwas then used to calculate flexural rigidity. Although the cantilevertest is a way to easily measure the stiffness of all fabrics, it isimportant to be able to correlate the results with consumer opinion. Thefeel of a fabric in a persons hand may have different properties thanthat found in a mechanical test. In addition, the surface of the fabricshould have a soft feel to the touch as well.

[0122] All handfeel evaluations were conducted by a panel of 12 who werechosen to make evaluations on the graininess and stiffness of thefabrics. All panelists followed the following procedure:

[0123] 1. Each panelist was given 4 anchor samples and theircorresponding number ranging from 1 for the least grainy or least stiffto 15 for the most stiff or most grainy. The anchors and theircorresponding numbers are given in Table 10.

[0124]2. The panelist laid the sample flat on the table with theembossed side of the fabric face up. Their wrist lay on the table topand their index and middle fingers moved across the entire surface ofthe sample. This process was repeated in all four directions of thesample. Their evaluation rating for graininess was recorded.

[0125] 3. The panelist laid the sample flat on a table with theirdominant hand on top of the sample. Their fingers were positioned so thefingers are pointed toward the top of the sample. The sample wasgathered with fingers moving toward their palm while the opposite handguided the sample into a cupped hand. The sample is squeezed andreleased repeatedly.

[0126] 4. Their evaluation rating was recorded for stiffness.

[0127] All samples were evaluated before a number rating was given foreach. Due to the availability of panelists only a selected set ofsamples were tested.

Example 1

[0128] Polyethylene (PE) polymers were obtained from The Dow ChemicalCompany. The polyethylene polymers have varying density and meltindices. A polypropylene (PP) polymer also was obtained from The DowChemical Company. The properties of the polymers are given in Table 1.TABLE 1 Polymers Used in Experiments Melt Index Polymer Grade Density(g/cc) (g/10 minutes) Melt Point (° C.) PE1 0.955 29 131 PE2 0.941 27125 PE3 0.950 17 129 PE4 0.870  1  55 PP1 0.910 35 165

[0129] Polyethylene that is representative of PE1 include ASPUN™ 6842Aavailable from The Dow Chemical Company, Midland, Mich. Polyethylenethat is representative of PE2 include ASPUN™ 6811 available from The DowChemical Company, Midland, Mich. Polyethylene that is representative ofPE3 include ASPUN™ 6835A available from The Dow Chemical Company,Midland, Mich. Polyethylene that is representative of PE4 includeAFFINITY™ EG8100 available from The Dow Chemical Company, Midland, Mich.Polypropylene that is representative of PP1 include H500-35 availablefrom The Dow Chemical Company, Midland, Mich. Four samples wereformulated from the polyethylene polymers. Three homopolymers and a 95percent/5 percent blend of PE1 and PE4 were tested. Compounding for theblend was as described above. 4.75 kg of PE1 pellets were combined with0.25 kg of PE4 and placed in the hopper of the twin screw extruder.After exiting the extruder, the polymer is pulled through a cooling bathmaintained at 5° C. The solid polymer is then fed into a Berlyn ClayGroup chipper where it is cut into pellets. The polymer was purged for15 minutes and pellets were collected for 100 minutes.

[0130] Fibers were produced using the spinning conditions given in Table2 and the process described above. TABLE 2 Spinning Conditions forVarious Fibers Predicted Total Extruder Godet Godet Fiber Mass of Temp.Speed Speed Diameter Sample Fiber Polymer (° C.) (rpm) (m/min) (microns)(g) 1 PE1 190 1800 900 21 540 2 PE2 190 1800 900 21 180 3 PE3 190 1800900 21 180 4 PE1 + PE4 190 1800 900 21 180 5 PP1 230 1800 900 21 180

[0131] Fabrics were produced from the above described processes usingthe fibers produced in Table 1 and were coded in the following manner. Aseries of three numbers was assigned to each sample. The first numberindicated the polymer used. The second number indicated the bond patternnumber and the third number indicated the bonding temperature. Refer toTable 2 for reference to the polymer number and FIGS. 3A-3I forreference to bond pattern numbers. For convenience, this labeling systemis used to identify samples.

[0132]FIG. 3A is for bond pattern 1 having a 46° angle, 20 percent bondarea, 3.44×10⁵ pts/m2 (222 pts/in²), base width of 1.7×10⁻³ m (0.067inch), base height of 4.32×10⁻⁴ m (0.017 inch), and a point width of7.62×10⁻⁴ m (0.03 inch). FIG. 3B is for bond pattern 2 having a20°angle, 16 percent bond area, 3.44×10⁵ pts/m² (222 pts/in²), basewidth of 1.7×10⁻³ m (0.067 inch), base height of 4.32×10⁻⁴ m (0.017inch), and a point width of 6.86×10⁻⁴ m (0.027 inch). FIG. 3C is forbond pattern 3 having a 20° angle, 24 percent bond area, 3.44×10⁵ pts/m²(222 pts/in²), base width of 1.7×10⁻³ m (0.067 inch), base height of4.32×10⁻⁴ m (0.017 inch), and a point width of 8.38×10⁻⁴ m (0.033 inch).FIG. 3D is for bond pattern 4 having a 20° angle, 20 percent bond area,2.31×10⁵ pts/m² (149 pts/in²), base width of 1.7×10⁻³ m (0.067 inch),base height of 4.32×10⁻⁴ m (0.017 inch), and a point width of 9.30×10⁻⁴m (0.0366 inch). FIG. 3E is for bond pattern 5 having a 20° angle, 20percent bond area, 4.60×10⁵ pts/m² (297 pts/in²), base width of 1.7×10⁻³m (0.067 inch), base height of 4.32×10⁻⁴ m (0.017 inch), and a pointwidth of 6.60×10⁻⁴ m (0.026 inch). FIG. 3F is for bond pattern 6 havinga 42° angle, 16 percent bond area, 3.44×10⁵ pts/m² (222 pts/in²), basewidth of 1.7×10⁻³ m (0.067 inch), base height of 4.32×10⁻⁴ m (0.017inch), and a point width of 6.86×10⁻⁴ m (0.027 inch). FIG. 3G is forbond pattern 7 having a 37° angle, 24 percent bond area, 3.44×10⁵ pts/m²(222 pts/in²), base width of 1.7×10⁻³ m (0.067 inch), base height of4.32×10⁻⁴ m (0.017 inch), and a point width of 8.38×10⁻⁴ m (0.033 inch).FIG. 3H is for bond pattern 8 having a 46° angle, 20 percent bond area,2.31×10⁵ pts/m² (149 pts/in²), base width of 1.7×10⁻³ m (0.067 inch),base height of 4.32×10⁻⁴ m (0.017 inch), and a point width of 9.3×10⁻⁴ m(0.0366 inch). FIG. 3I is for bond pattern 9 having a 35° angle, 20percent bond area, 4.60×10⁵ pts/m² (297 pts/in²), base width of 1.7×10⁻³m (0.067 inch), base height of 4.32×10⁻⁴ m (0.017 inch), and a pointwidth of 6.60×10⁻⁴ m (0.026 inch).

[0133] Next, pieces of fabric were cut for tensile testing, abrasiontesting, and a cantilever test. All samples were cut from the center dueto inconsistency in the fiber web and processing temperature at theedges.

[0134] The fabrics were visually evaluated. Temperature, pressure andresin choice had no effect on the visual appearance of the fabric. Bondroll pattern had a noticeable effect on the fabric's visual property.FIGS. 4A-4I are micrographs at 20× magnification of nonwovens producedfrom resin 6824A at 119.4° C. (247° F.) which show the differences inthe fabrics visually. The dark diamond areas are the bond areas of thefabrics, while the lighter areas are unbonded fibers.

[0135] A comparison of FIGS. 4A, 4F, 4G, 4H and 4I to FIGS. 4B, 4C, 4D,and 4E show that a side wall angle of 20° produces a smaller bond areathan that of patterns that contain a larger side wall angle.Measurements of the bond site areas of the fabric are given in Table 3.The data show a greater percent bond area than the roll pattern thatproduced the fabric in bond patterns 1, 6, 7 and 8. This is due to themelt flow of polymer from under the bond pin and also the increased heattransfer due to compaction of fibers in the void areas between the bondpins. The fibers contain less free space and heat transfer viaconduction is higher. All patterns containing 20° side wall angles showa fabric percent bond area less than that of the roll pattern. Shrinkageof the polymer fibers is a possible cause. During the spinning processof the fibers, the fibers are solidified under tension in an orientedstate. When the fibers are exposed to the higher temperatures under thebond pins, the polymer molecules relax back or shrink to a more stablestate. TABLE 3 Measured Bond Areas of Nonwoven Samples TemperatureAverage percent Resin Pattern ° C. (° F.) bond area PE1 1 119.4 (247)33.7 PE1 2 119.4 (247) 16.5 PE1 3 119.4 (247) 30.8 PE1 4 119.4 (247)19.0 PE1 5 119.4 (247) 20.7 PE1 6 119.4 (247) 17.7 PE1 7 119.4 (247)31.8 PE1 8 119.4 (247) 24.7 PE1 9 119.4 (247) 24.1 PE2 1 116.1 (241)31.1 PE2 2 116.1 (241) 14.0 PE2 3 116.1 (241) 20.7 PE2 4 116.1 (241)17.6 PE2 5 116.1 (241) 17.5 PE2 6 116.1 (241) 17.1 PE2 7 116.1 (241)28.6 PE2 8 116.1 (241) 22.2 PE2 9 116.1 (241) 23.1 PE3 1 119.4 (247)33.0 PE3 2 119.4 (247) 13.8 PE3 3 119.4 (247) 23.5 PE3 4 119.4 (247)15.5 PE3 5 119.4 (247) 17.3 PE3 6 119.4 (247) 16.3 PE3 7 119.4 (247)28.4 PE3 8 119.4 (247) 23.2 PE3 9 119.4 (247) 19.8 95 percent PE1 + 1119.4 (247) 30.8 5 percent PE4 95 percent PE1 + 2 119.4 (247) 13.4 5percent PE4 95 percent PE1 + 3 119.4 (247) 19.0 5 percent PE4 95 percentPE1 + 4 119.4 (247) 17.0 5 percent PE4 95 percent PE1 + 5 119.4 (247)16.5 5 percent PE4 95 percent PE1 + 6 119.4 (247) 15.3 5 percent PE4 95percent PE1 + 7 119.4 (247) 26.8 5 percent PE4 95 percent PE1 + 8 119.4(247) 21.8 5 percent PE4 95 percent PE1 + 9 119.4 (247) 20.0 5 percentPE4

[0136] The 20° side wall angle patterns also appear to have fibers thatare less compacted together or a higher porosity. Bond patterns 4, 5, 7and 8 have the same percent bond area, but different concentrations ofpoints per square meter. The distance between each bond point is greaterfor the patterns with the lower concentration of points per squaremeter.

[0137] An analysis of the fabric weight is shown in Table 4. Due to thevariation in the carding process and the handling of fiber webs, thinspots appear in the fabric. Variability in thickness can have a strongimpact on mechanical properties. The weight of one square inch sampleswithin a fabric has very low variability. TABLE 4 Analysis of FabricWeight Between and Within Samples Resin Pattern Average Weight (g) PE1 10.021 PE1 2 0.023 PE1 3 0.023 PE1 4 0.020 PE1 5 0.019

[0138] FIGS. 4A-4I are micrographs of varying bond patterns of PE1 resinat 119.4° C. (247° F.) that were also used to evaluate fiberorientation. A study of the figures show most of the fibers arranged inone direction (up and down). This is the machine direction (MD) of thefibers. Most spunbond and meltdown fabrics contain more of a randomarrangement of fibers so that the fabric contains cross direction (CD)strength as well as machine direction strength. An evaluation ofrandomly selected fabrics showed that fabric orientation (f_(p)) valuesfor a commercial spunbond fabric were much lower than that of thesamples produced and tested in these examples. The commercial spunbondfabric was made from polypropylene at TANDEC. The results are given inTable 5. The f_(p) values at the bottom of the fabric are higher thanthat of the top meaning the fibers are more aligned in the machinedirection on the bottom. The bond pins on the top pushes the fibers intoa more random state while the bottom fibers bonded against a flat rollmaintain the alignment of the web. TABLE 5 Data Collected fromOrientation of Fibers Measurement Fabric f_(p) (1) f_(p) (2) f_(p) (3)Average f_(p) PE (Top) 0.56 0.54 0.53 0.54 PE (Bottom) 0.7 0.82 0.690.74 Spunbond PP 0.22 0.19 0.25 0.22 Spunbond PP 0.16 0.18 0.22 0.19

[0139] Tables 6 through 9 show various properties of the nonwovenfabrics for each polymer fiber tested using various bond patterns atvarious temperatures. A series of three numbers was assigned to eachsample. The first number indicates the polymer used. The second numberindicates the bond pattern number and the third number indicates thebonding temperature in ° F. Refer to Table 2 for reference to thepolymer number and FIGS. 3A-3I for reference to bond pattern numbers.For convenience, this labeling system is used to identify samples. Forexample, 1-1-116.1 stands for fabric made of PE1 resin using bondpattern 1 (FIG. 3A) at a bonding temperature of 116.1° C. (241° F.).Tensile properties of all samples were measured for peak load andelongation at break using an Instron 4501 and procedure ASTM D 5035-90as previously described. Due to variability between fabrics produced atthe same conditions 6 tensile samples were tested. The average abrasion(ABR) observed at each of the processing conditions is listed. Forflexural rigidity (FR), each fabric was measured for length of overhangalong with its basis weight to determine FR according to ASTM D 1388-64as described above. The average FR measured of each resin with eachprocessing condition is listed. TABLE 6 Data for Resin PE1 Avg. percentNormalized Avg. Avg. Abrasion Avg. FR Sample Elongation Peak Load (g)(mg/cm²) (mg*cm) 1-1-116.1 43.17 1974 0.76 29.1 1-1-117.7 52.20 20260.71 33.8 1-1-119.4 70.00 2161 0.55 45.9 1-2-116.1 16.77 920 1.02 17.61-2-117.7 17.40 882 1.01 20.3 1-2-119.4 31.61 1186 0.83 22.0 1-2-116.117.00 927 0.77 30.4 1-3-117.7 20.06 1032 0.71 28.8 1-3-119.4 27.81 13300.53 33.6 1-4-116.1 20.73 956 1.08 17.8 1-4-117.7 19.66 915 0.92 19.61-4-119.4 27.64 1141 0.64 19.6 1-5-116.1 9369 806 0.99 17.9 1-5-117.70.89 25.3 1-5-119.4 19.37 1073 0.66 32.4 1-6-116.1 32.08 1253 0.93 28.41-6-117.7 49.86 1393 0.89 38.4 1-6-119.4 76.48 1619 0.75 50.8 1-7-116.141.15 1511 0.72 48.0 1-7-117.7 52.51 1821 0.66 51.4 1-7-119.4 93.13 21490.54 70.1 1-8-116.1 48.27 1517 0.97 41.4 1-8-117.7 75.35 1666 0.83 46.21-8-119.4 70.34 1865 0.61 56.0 1-9-116.1 24.08 1193 0.94 45.7 1-9-117.728.04 1335 0.85 55.6 1-9-119.4 53.75 1493 0.64 85.2

[0140] TABLE 7 Data for Resin PE2 Avg. percent Normalized Avg. Avg.Abrasion Avg. FR Sample Elongation Peak Load (g) (mg/cm²) (mg*cm)2-1-112.7 24.62 1646 0.94 31.8 2-1-114.4 31.54 1912 0.80 43.3 2-1-116.145.24 2075 0.68 66.2 2-2-112.7 49.30 1228 1.20 30.1 2-2-114.4 60.96 13360.92 36.7 2-2-116.1 36.26 1188 0.75 50.3 2-3-112.7 63.42 1370 1.00 35.92-3-114.4 62.79 1544 0.74 41.8 2-3-116.1 33.12 1336 0.59 55.1 2-4-112.781.15 1482 1.06 20.2 2-4-114.4 90.96 1525 0.78 24.2 2-4-116.1 39.15 13160.65 35.9 2-5-112.7 54.37 1409 0.97 35.0 2-5-114.4 64.09 1508 0.84 40.12-5-116.1 19.75 1344 0.61 51.5 2-6-112.7 74.57 1530 1.06 39.6 2-6-114.456.29 1438 0.93 52.8 2-6-116.1 38.05 1057 0.75 57.4 2-7-112.7 68.12 15830.96 43.0 2-7-114.4 64.24 1743 0.78 54.3 2-7-116.1 50.48 1858 0.58 72.52-8-112.7 95.53 1594 1.04 35.5 2-8-114.4 91.61 1617 0.75 40.3 2-8-116.133.78 1122 0.65 48.6 2-9-112.7 60.33 1685 0.95 54.6 2-9-114.4 78.11 17050.83 54.1 2-9-116.1 73.58 1950 0.61 60.8

[0141] TABLE 8 Data for Resin PE3 Avg. percent Normalized Avg. Avg.Abrasion Avg. FR Sample Elongation Peak Load (g) (mg/cm²) (mg* cm)3-1-116.1 17.74 1447 0.92 40.0 3-1-117.7 21.50 1702 0.61 41.0 3-1-119.427.82 1919 0.55 46.3 3-2-116.1 13.53 1242 1.09 41.4 3-2-117.7 23.23 17850.97 40.1 3-2-119.4 32.40 1992 0.79 46.0 3-2-116.1 21.65 1922 0.89 36.83-3-117.7 28.69 2021 0.62 44.8 3-3-119.4 40.03 2274 0.56 44.9 3-4-116.122.66 1721 1.06 27.7 3-4-117.7 26.83 1845 0.89 38.7 3-4-119.4 38.57 20350.69 42.1 3-5-116.1 12.33 1248 1.05 28.8 3-5-117.7 16.31 1582 0.87 35.43-5-119.4 28.89 1975 0.70 40.3 3-6-116.1 18.79 1138 1.03 60.4 3-6-117.728.29 1677 0.88 88.4 3-6-119.4 41.52 1980 0.80 98.0 3-7-116.1 24.87 15970.94 82.9 3-7-117.7 41.28 1879 0.66 90.1 3-7-119.4 51.97 2376 0.55 125.53-8-116.1 26.63 1255 0.97 74.1 3-8-117.7 43.24 1806 0.81 79.9 3-8-119.436.78 2017 0.68 88.4 3-9-116.1 16.56 904 0.90 80.7 3-9-117.7 16.83 12790.84 103.7 3-9-119.4 20.26 1456 0.65 116.4

[0142] TABLE 9 Data for Resin Containing 95 percent PE1 and 5 percentPE4 Avg. percent Normalized Avg. Avg. Abrasion Avg.FR Sample ElongationPeak Load (g) (mg/cm²) (mg*cm) 4-1-116.1 54.03 2065 0.96 22.9 4-1-117.781.32 2288 0.75 35.8 4-1-119.4 31.72 1988 0.50 39.0 4-2-116.1 20.23 13221.09 32.6 4-2-117.7 33.20 1659 1.00 42.0 4-2-119.4 33.48 1676 0.72 53.44-2-116.1 27.46 1485 0.95 35.3 4-3-117.7 36.27 1735 0.71 32.6 4-3-119.451.98 2192 0.53 49.0 4-4-116.1 27.59 1452 1.33 26.5 4-4-117.7 39.67 17561.05 30.3 4-4-119.4 42.27 1928 0.77 29.4 4-5-116.1 19.75 1344 1.28 31.04-5-117.7 34.79 1800 1.03 47.7 4-5-119.4 41.19 2017 0.70 48.7 4-6-116.134.41 1590 0.97 56.9 4-6-117.7 60.42 1812 0.84 71.0 4-6-119.4 28.85 15890.63 91.0 4-7-116.1 49.89 1920 0.93 67.9 4-7-117.7 75.67 2241 0.73 82.04-7-119.4 32.57 1861 0.48 102.7 4-8-116.1 54.02 1862 0.99 46.5 4-8-117.745.77 2076 0.85 62.4 4-8-119.4 46.92 1884 0.64 77.9 4-9-116.1 29.05 13621.03 67.7 4-9-117.7 53.70 1737 0.85 80.7 4-9-119.4 57.83 1862 0.58 109.6

[0143] Peak load values ranged from 800 g to as high as 2400 g. Thesevalues are much less than a typical PP sample. Using pattern 2 at 136.6°C. (278° F.), PP1 produces a peak load of 4875 g. In general, thenormalized peak load increases with an increase in temperature, bondarea, and bond angle. For resin PE2 and the blend of 95 percent PE1 and5 percent PE4 the peak load decreased when increasing the temperaturefrom 114.4° C. (238° F.) to 116.1° C. (241° F.) for PE2 and from 117.7°C. (244° F.) to 119.4° C. (247° F.) for the blend. This may becontributed to a change in the fracture mechanism. The pairwisecomparison of samples shows that a 24 percent bond area has a higherpeak load than the 16 percent bond area. As shown earlier, the bondangle has a dramatic effect on the actual bond area on the samples. FIG.5 is a graph of normalized peak load versus temperature of PE2 resin atdifferent temperatures and using various bond patterns. The peak loadwas linearly normalized to a basis weight of 33 g/m²(1 oz/yd²) becausepeak load is a strong function of basis weight.

[0144]FIG. 6 is a graph of percent elongation versus temperature forresin PE2 at different temperatures using various bond patterns. Theelongation of PE nonwovens ranged from 10 percent to as high as 95percent. Using pattern 2 at 136.6° C. (278° F.), the elongation of PPonly reached 31 percent and 37 percent was the highest value reached atany process condition. A decrease in the concentration of bond pointsincreases the elongation significantly. In fact, resin PE2 almostdoubled its elongation at 114.4° C. (238° F.) with a decrease inconcentration of bond points from 4.60×10⁵ pts./m² to 2.31×10⁵ pts./m²(297 pts./in² to 149 pts./in.²). The exception to this is resin of 95percent PE1 and 5 percent PE4 which does not show a large difference inelongation with decreasing concentration of bond points. This can beexplained by the highly elastic property of PE4 that could be moresignificant than the effect of the bond pattern. Temperature control isimportant. A 1.6° C. (3° F.) difference in temperature can have as muchas a 100 percent decrease in elongation.

[0145] Three examples of typical stress-strain curves for resin PE1 aregiven in FIG. 7. The samples were manufactured using PE1 resin usingbond pattern 3 at temperatures of 116.1° C. (241° F.), 117.7° C. (244°F.), and 119.4° C. (247° F.). As the temperature increases so does thepeak load. At the highest temperature of 119.4° C. (247° F.), theelongation of the fabric decreases. Also the initial modulus of thefabric produced at 119.4° C. (247° F.) is higher than those produced atlower temperatures. This is typical of all the fabric samples.

[0146]FIG. 8 is a typical graph of abrasion versus temperature for resinPE1. In general, the data show that elongation is a function of allprocessing variables. An increase in bond area and bond angle which areinterrelated increases the elongation of the fabric. In general theabrasion resistance is mostly a function of temperature, althoughsignificant differences can be seen between bond patterns. This may beexplained by its fracture mechanism. As the surface is abraded, thefibers are pulled from the bond points. Because of the fracturemechanism for abrasion, the amount of fuzz on the surface depends onbond strength more than the size of the bond. The values for abrasionranged from 0.48 mg/cm² to greater than 1 mg/cm². A PP sample using bondpattern 2 at 136.6° C. (278° F.) has an abrasion value of 0.15 mg/cm²,over 3 times less than that of PE.

[0147] A plot of flexural rigidity (“FR”) vs. temperature is shown asFIG. 9 for resin PE2. This is a typical plot and represents the trendsfound in the other resins. A high length of overhang indicates a stifffabric. Also, a high basis weight contributes to an increase instiffness since the fabric supports a larger weight as it hangs over theedge. An average of the fabric's overhang with the engraved roll sidefacing up and facing down was considered the total overhang for anindividual piece of fabric. An average of each was taken. This isthought to better represent the overall stiffness of the fabric sincethe fabric bends in both directions during wear. Four measurements weretaken for each sample in this manner.

[0148] It is observed that bond patterns 6-9 with larger bond angleshave higher values than patterns 2-5 with 20° bond angles. The flexuralrigidity of all the PE samples ranged from the low twenties to a high of125 mg*cm for sample 3-7-119.4. These values are relatively low,considering a typical PP fabric has a FR value of over 200 mg*cm. ResinPE2 showed the least stiffness when compared to other resins of the sameprocessing conditions. This is likely due to the low density of thepolymer. The highest FR values were obtained by PE3 and can beattributed to a higher polymer density. The addition of PE4 to PE1produced a higher FR values. It is likely due to an increase in meltingin the bond area and/or shrinkage of the fibers and fabric. Concerningthe bond pattern, it is shown that low bond areas, low side wall angles,and low bond point concentrations produce the lowest values of FR. Itshould be noted that low bond areas, side wall angles, and bond pointconcentrations can affect other properties, i.e., abrasion. Therefore,due to PE's low modulus, the FR value may not be as important as otherproperties.

[0149] The effect that bond roll patterns have on the stiffness (ST) ofthe fabric and the graininess (GR) of the surface was evaluated by thehandfeel test. 12 panelists rated the two properties on a scale of 1 to15. Anchors (used as a baseline) were provided as listed in Table 10.Resin PE1 processed at 119.4° C. (247° F.) on each bond pattern wereused as samples. Table 11 summarizes the averages of the two handratings for each bond pattern. TABLE 10 Anchor Materials and theirCorresponding Value Test Type Anchor Material Anchor Number GrainyBleached mercerized cotton poplin 2.1 Grainy Army carded cotton sateen4.9 bleached Grainy Cotton momie fabric 9.5 Grainy Cotton duck greige13.6 Stiffness Polyester/cotton 50/50 single knit 1.3 Stiffness Bleachedmercerized cotton print 4.7 cloth Stiffness Bleached mercerized cottonpoplin 8.5 Stiffness Cotton organdy 14.0

[0150] TABLE 11 Data Collected for Hand Survey Sample Stiffness Grainy1-1-119.4 2.5 5.6 1-2-119.4 0.9 2.9 1-3-119.4 1.8 3.9 1-4-119.4 1.6 4.01-5-119.4 1.1 2.8 1-6-119.4 1.7 3.5 1-7-119.4 3.0 5.4 1-8-119.4 1.5 4.01-9-119.4 2.5 4.9 5-2-140 5.3 6.4

[0151] Scanning Electron Microscopy (SEM) was used to analyze theeffects of processing conditions on the nonwoven surface, bondperimeter, cross section and failure mechanism. It has been shown thatprocessing conditions effect the feel and the strength of the fabric.This section discusses the relationship between the fabric surface andits properties and also identifies the fracture mechanisms as a functionof processing conditions.

[0152] Arial views and cross-section views were obtained using thefollowing procedure:

[0153] 1. The cross-section of the fabric was cut by placing it betweentwo pieces of paper and placing the sample into liquid nitrogen forabout 1 min, followed by cutting with a razor blade perpendicular to themachine direction.

[0154] 2. The sample was placed on a stage with conductive tape and theedges were lined with conductive graphite paint.

[0155] 3. A Denton Vacuum Hi-Res 100 high-resolution chromium sputteringsystem was used to coat the fabric with 100-120 Angstroms thick film.

[0156] 4. The sample was placed in the sample compartment and thecompartment was evacuated to 1.3×10⁻⁵ Pa (10⁻⁷ torr).

[0157] 5. 5 kEV was used out of the 20 kEV available due to problemswith charge buildup on the fabric surface.

[0158] 6. Micrographs were obtained at various magnifications.

[0159] 7. Scion imaging software was used to view and measure themicrograph images.

[0160] All tested samples were micrographed at a low magnification ofbetween 60× and 100× focusing on the bond point. Since there was nonoticeable surface difference between temperatures, all pictures weretaken of samples at 1.6° C. (3° F.) below their stick point. Thistemperature is 119.4° C. (247° F.) for all samples except for resin PE2which was at 119.4° C. ( 247° F.). All nine bond patterns made fromresin PE1 are shown in FIGS. 10A-10J. All bond points contain a largeflat surface in the middle that raises up toward the edge. Patterns 1,6, 7 and 8 all contain a large side wall angle. The effect of this isnot nearly as noticeable with the PE1 resin as it is in the otherresins, probably due to its high melt index. The patterns with the smallside wall angle produce a bond that contains a smaller flat area and,geometrically, a more rounded bond point. Because the shape of the bondpoint produced with a 20 degree side wall angle is rounded and coversless surface area as shown previously, then the space between each bondpoint is larger. This larger space gives the fabric its softer feel dueto the increase in exposure area of the fibers. This correlates wellwith the handfeel evaluation data. Conversely, the small bond pointsurface coverage produces less entangled fibers and decreased the fabricstrength. This was seen previously in tensile data.

[0161] One effect of processing conditions on the nonwoven fabric is itsfailure mechanism during destructive testing such as tensile andabrasion testing. Three types of failure can occur. The fibers can pullout of the bond sight, break at the bond perimeter, or break away fromthe bond. SEM micrographs were also used to identify the failuremechanism for selected nonwoven samples. FIGS. 11A-C shows examples ofthe failure mechanisms during tensile failure. Notice that mostprocessing conditions cause the polyethylene fabric to fail by thefibers pulling away from a weak bond point. In some cases at highertemperatures it was evident that the bonds were strong enough to causefiber breakage at the bond perimeter. The addition of 5 percent the PE4resin to the PE1 resin increased the bond strength enough at 119.4° C.(247° F.) to cause some fibers to break at the bond perimeter. There wasevidence of two fracture mechanisms at this point including fiberspulling away from the bond and fibers breaking at the perimeter.

[0162] An analysis of failure mechanisms caused by abrasion showed nosign of failure by breaking at the bond perimeter. FIGS. 12A-B show twoexamples of a fractured bond point caused by abrasion. The thinribbon-like strips are remnants of the previously thermally bondedpoint. Even those samples that failed in tensile tests by brittle fiberfailure at the bond perimeter did not show the same fracture mechanism.After abrasion the fabric failed by destruction of the bond point. Thisphenomena may explain why abrasion resistance does not reach a peakvalue and then decrease as the processing temperature is increased asdoes the tenacity and elongation. The abrasion resistance is dependentonly on the bond strength.

[0163] As demonstrated above, embodiments of the invention provide anonwoven fabric which has relatively increased tensile strength,elongation, abrasion resistance, flexural rigidity, and/or softness.Additional characteristics and advantages provided by embodiments of theinvention are apparent to those skilled in the art.

[0164] While the invention has been described with reference to alimited number of embodiments, variations and modifications therefromexist. For example, the fabric composition need not be a mixture withinthe compositions given above. It can comprise any amount of components,so long as the properties desired in the fabric composition are met. Itshould be noted that the application of the fabric composition is notlimited to sanitary articles; it can be used in any environment whichrequires a thermally bonded nonwoven fabric. The appended claims intendto cover all such variations and modifications as falling within thescope of the invention.

What is claimed is:
 1. A method of making a non-woven fabric,comprising: passing a fiber web through a pair of rolls to obtain athermally bonded fabric with a high percentage of bond areas, whereinthe high percentage of bond areas is formed by an engraved pattern onone of the rolls, and the engraved pattern has a high percentage of bondpoint areas.
 2. The method of claim 1, wherein the engraved pattern hasa high percentage of bond point area and a wide bond point angle.
 3. Themethod of claim 1, wherein the percentage of bond areas is at leastabout 16 percent.
 4. The method of claim 1, wherein the percentage ofbond areas is at least about 20 percent.
 5. The method of claim 1,wherein the percentage of bond areas is at least about 24 percent. 6.The method of claim 2, wherein the bond point angle is about 20° orhigher.
 7. The method of claim 2, wherein the bond point angle is about35° or higher.
 8. The method of claim 2, wherein the bond point angle isabout 37° or higher.
 9. The method of claim 2, wherein the bond pointangle is about 42° or higher.
 10. The method of claim 2, wherein thebond point angle is about 46° or higher.
 11. The method of claim 1,wherein the engraved pattern has at least about 1.55×10⁵ bond points persquare meter.
 12. The method of claim 1, wherein the engraved patternhas at least about 2.31×10⁵ bond points per square.
 13. The method ofclaim 1, wherein the engraved pattern has at least about 3.1×10⁵ bondpoints per square meter.
 14. The method of claim 1, wherein the engravedpattern has at least about 3.44×10⁵ bond points per square meter. 15.The method of claim 1, wherein the engraved pattern has at least about4.6×10⁵ bond points per square meter.
 16. The method of claim 1, whereinthe engraved pattern has at least about 4.65×10⁵ bond points per squaremeter.
 17. The method of claim 1, 4, 7, or 14, wherein the fiber webcomprises polyethylene.
 18. The method of claim 17, wherein thepolyethylene is a homopolymer of ethylene.
 19. The method of claim 17,wherein the polyethylene is a copolymer of ethylene and a comonomer. 20.The method of claim 17, wherein the polyethylene is obtained in thepresence of a metallocene catalyst.
 21. The method of claim 17, whereinthe polyethylene is obtained in the presence of a constrained geometrycatalyst.
 22. The method of claim 17, wherein the polyethylene isobtained in the presence of a single site catalyst.
 23. A non-wovenfabric comprising a polymer, wherein the fabric is characterized by ahigh percentage of bond areas and a high abrasion resistance.
 24. Thenon-woven thermal bonding fabric of claim 23, wherein the polymer ispolyethylene.
 25. The method of claim 23, wherein the percentage of bondareas is at least about 16 percent.
 26. The method of claim 23, whereinthe percentage of bond areas is at least about 20 percent.
 27. Themethod of claim 23, wherein the percentage of bond areas is at leastabout 24 percent.
 28. A fabric made by the method, comprising: passing afiber web through a pair of rolls to obtain a thermally bonded fabricwith a high percentage of bond areas, wherein the high percentage ofbond areas is formed by an engraved pattern on one of the rolls, and theengraved pattern has a high percentage of bond point areas.
 29. Thefabric of claim 28, wherein the engraved pattern has a wide bond pointangle.
 30. The fabric of claim 28, wherein the percentage of bond areasis at least about 16 percent.
 31. The fabric of claim 28, wherein thepercentage of bond areas is at least about 20 percent.
 32. The fabric ofclaim 28, wherein the percentage of bond areas is at least about 24percent.
 33. The fabric of claim 29, wherein the bond point angle isabout 20 degrees or higher.
 34. The fabric of claim 29, wherein the bondpoint angle is about 35 degrees or higher.
 35. The fabric of claim 29,wherein the bond point angle is about 37 degrees or higher.
 36. Thefabric of claim 29, wherein the bond point angle is about 42 degrees orhigher.
 37. The fabric of claim 29, wherein the bond point angle isabout 46 degrees or higher.
 38. The fabric of claim 28, wherein theengraved pattern has at least about 1.55×10⁵ bond points per squaremeter.
 39. The fabric of claim 28, wherein the engraved pattern has atleast about 2.31×10⁵ bond points per square meter.
 40. The fabric ofclaim 28, wherein the engraved pattern has at least 3.1×10⁵ bond pointsper square meter.
 41. The fabric of claim 28, wherein the engravedpattern has at least about 3.44×10⁵ bond points per square meter. 42.The fabric of claim 28, wherein the engraved pattern has at least about4.6×10⁵ bond points per square meter.
 43. The fabric of claim 28,wherein the engraved pattern has at least about 4.65×10⁵ bond points persquare meter.
 44. The fabric of claim 28, 31, 34, or 41, wherein thefiber web comprises polyethylene.
 45. The fabric of claim 43, whereinthe polyethylene is a homopolymer of ethylene.
 46. The fabric of claim43, wherein the polyethylene is a copolymer of ethylene and a comonomer.47. The fabric of claim 43, wherein the polyethylene is obtained in thepresence of a metallocene catalyst.
 48. The fabric of claim 43, whereinthe polyethylene is obtained in the presence of a constrained geometrycatalyst.
 49. The fabric of claim 43, wherein the polyethylene isobtained in the presence of a single site catalyst.
 50. A method ofmaking a non-woven polyethylene fabric, comprising: passing apolyethylene fiber web through a pair of rolls to obtain a thermallybonded fabric with at least 20 percent of bond areas, wherein the bondareas is formed by an engraved pattern on one of the rolls, and theengraved pattern has at least about 3.1×10⁵ bond points per squaremeter.
 51. The method of claim 50, wherein the engraved pattern has abond point angle of about 20° or higher.
 52. The method of claim 51,wherein the bond point angle is about 35° or higher.
 53. The method ofclaim 51, wherein the bond point angle is about 37° or higher.
 54. Themethod of claim 51, wherein the bond point angle is about 42° or higher.55. The method of claim 51, wherein the bond point angle is about 46° orhigher.
 56. The method of claim 50, wherein the engraved pattern has atleast about 3.44×10⁵ bond points per square meter.
 57. The method ofclaim 50, wherein the percentage of bond areas is at least about 24percent.